In general, this invention relates to the processing of digital data and more particularly, this invention relates to the conversion of NRZ digital data into BRZ digital data which is frequency modulated in a synchronous manner, for recording on magnetic tape.
Motion analysis of fast moving phenomena in slow motion entails the recording of a great number of images during an event at high speed, and then playing the images back slowly to analyze the movement which has occurred in step-by-step progression. Applications for motion analysis include malfunctions in high speed machinery, movements of an athlete, failure of safety equipment, shattering of an object and physical reactions to a tire hitting a pothole at high speed. One type of motion analyzer includes a video camera, a variable speed magnetic tape processor and a cathode ray tube (CRT) display monitor. The camera is capable of producing signals corresponding to selected frame rates of from 60 to about 2000 frames per second. The magnetic tape processing system is capable of recording at one tape speed and appropriately slowing down the tape during playback to a certain predetermined speed to down convert the camera signals regardless of the camera frame rate, to a nominal frame rate of 30 or 60 frames per second. The CRT display monitor receives the second frame rate playback signal from the magnetic tape processing system and displays the scene in question at an appropriate slow motion, depending upon the selected camera frame rate.
The display monitor of such a motion analyzer may be provided with a data frame border which displays various items of information recorded on the tape with each frame image. Such items of information include the time of day and date on which the frame was recorded, the elapsed time since the beginning of the recording, a user entered identification number for each test, recording rate selected, a frame counter from beginning of recording, and other information relative to the scene being recorded. In such a magnetic tape processing system, the video information is recorded as FM signals on a plurality of parallel linear tracks on magnetic tape. A multigap record head and multigap reproduce head are utilized for recording and reproducing the video signals from the tape. In order to minimize the number of magnetic heads required to record and reproduce signals from the magnetic tape, it is desirable that the information relating to each frame be recorded in the minimum number of tracks on the magnetic tape. Since the data relating to information concerning a given frame is conventionally in the format of a non return to zero (NRZ) digital data signal, if the NRZ digital data signals were recorded directly on tape, a separate data rate timing signal would also have to be recorded on a separate track on the tape in order to accurately reproduce the recorded data. This necessitates the use of two tracks on the tape for the data, and thus increases the number of recording and reproducing heads and the width of tape required for recording the information data signal. It is thus desirable that digital data information be recorded on the magnetic tape in a single track in order to reduce recording space on the tape, and the number of recording and reproducing magnetic heads needed in the magnetic tape processor. Similarly, it is also desirable that efficient data packing densities on the tape is effected and that accurate synchronization information be recorded on the data track so that the data may be recovered in synchronism with the related video information.
Since the speed at which the video data is recorded on tape is variable in relation to the frame rate of recording, but the video information is played back at the same tape speed irrespective of the recording speed, it is also desirable that the data recording technique take into account the varying tape speeds at which the video information is recorded so that there will be constant data signal frequencies played back, thus simplifying the playback circuitry.
Thus it is desirable that, in recording and reproducing digital data, the reproduced digital data signal duplicate the original digital data signal so that accurate information relating to a frame is displayed on the monitor.